1. Field of the Invention
The present invention relates to an electric connection method for connection between a semiconductor substrate and an electric wiring substrate.
2. Description of the Related Art
Wire bonding and inner lead bonding (ILB) are examples of electric connection methods for a semiconductor substrate and an electric wiring substrate.
For example, the wire bonding is a method for electrically connecting a pad disposed on the semiconductor substrate and a wiring portion disposed on the electric wiring substrate with a metal wire. In general, gold or aluminum is used as a material for the pad, and gold or copper is used as a material for the wiring portion and the wire. The pad and the wire can be connected to each other by pressing and attaching the electric connection portion by heating the electric connection portion to a temperature above the melting points of the metallic materials. However, when damage caused by the heat to the semiconductor substrate is taken into consideration, it is desirable not to heat the electric connection portion to the temperature above the melting points of the metallic materials. An ultrasonic wave is generally used in combination with heat in order to connect the pad and the wire at low temperature. A method for forming an electric connection by using the ultrasonic wave in combination with heat is also used in the ILB.
On the other hand, various kinds of stress may be applied to the electric connection portion when a finished product is actually in use. The stress arising from expansion and contraction of the wire due to change in an environmental temperature may be given as an example. A stronger connection state has to be realized because the electric connection state should be maintained even if the stress is applied to the electric connection portion. Generally, in order to realize the electric connection portion maintaining a state capable of withstanding the stress that is applied to the electric connection portion when the product is actually in use, the electric connection portion is heated to a temperature equal to or higher than 150° C. even if the connection method using the ultrasonic wave in combination with heat is employed.
In a configuration in which a semiconductor substrate and an electric wiring substrate are disposed on a supporting substrate, a method in which an electric connection portion is heated via the supporting substrate by making a heater block contact with a back surface of the supporting substrate is generally employed as a method for heating the electric connection portion in the electric connection process. With this method, in a case where a material having low thermal conductivity is used for the supporting substrate, a long period of time is required to heat the electric connection portion to a desired temperature. Further, in a case where a material having low thermal resistance is used for the supporting substrate, the heating temperature depends on the thermal resistance of the supporting substrate, and thus the electric connection portion cannot be heated to a temperature necessary to realize the electric connection portion maintaining the firm connection state. These issues are present in the connection method in which the electric connection portion on the front surface of the supporting substrate is heated from the back surface thereof.
With respect to the above issues, Japanese Patent Application Laid-Open No. 7-22458 discusses a method for electrically connecting the electric connection portion by heating the electric connection portion with hot air blowing on the surface of the semiconductor substrate. Further, Japanese Patent Application Laid-Open No. 5-90355 discusses a method for electrically connecting the electric connection portion by causing the electric connection portion itself to generate heat by applying high-frequency electric current to the electric connection portion through two electrodes that make contact with the electric connection portion of the semiconductor substrate.
In the electric connection process, in order to adjust a position for making an electric connection with high precision, in general, a predetermined shape pattern on the semiconductor substrate and the electric wiring substrate is read by an image recording apparatus to perform a positional adjustment through image processing. When the surface of a semiconductor substrate is blown by the hot air of 150° C. as in the method discussed in Japanese Patent Application Laid-Open No. 7-22458, there arises a problem in stably performing a positional adjustment with high precision. In the above method, because of hot air passing through a space between the image recording apparatus and a point to be recorded, fluctuation occurs in the image to be recognized by the image recording apparatus.
Further, with the method disclosed in Japanese Patent Application Laid-Open No. 5-90355, in which the high-frequency electric current is applied to the electric connection portion of the semiconductor substrate, the problem in performing the positional adjustment is reduced because hot air does not pass through the space between the image recording apparatus and the point to be recorded. However, respective processes, such as making the electrodes contact with the electric connection portion, applying the high-frequency electric current to the electric connection portion, and separating the electrodes from the electric connection portion, have to be performed on the electric connection portion one by one. Thus, a long period of process time will be required in order to make a number of electric connections for a single semiconductor substrate.